This invention relates to a lubricating system and method for supplying lubricating and cooling oil to the crankshaft and rod bearings of an engine, to the bearings of a turbocharger mounted on the engine and to cooling jets associated with pistons reciprocally mounted in the engine.
Upon the start-up of an internal combustion engine, lubricating oil must be communicated to the crankshaft and rod bearings thereof immdeiately. In addition, it is common practice to employ a turbocharger in association with the engine, which has a common shaft attached between the turbine and compressor wheels thereof. The shaft is mounted for hi-speed rotation in annular bearing assemblies which also require immediate lubrication to prevent undue wear or damage thereto.
The time required to communicate lubricant to such bearings primarily depends upon the resistnce which the oil meets an its communciation through the various oil passages and bearing clearances while the oil pump is functioning to fill the system and build-up the required working pressures. During cold starts of the engine, such pressure build-up may take as long as 15 to 30 seconds. In many cases, such a time delay is sufficient to starve the bearings of lubricant and to thus cause damage to such bearings and attendant components of the engine.
A further problem may be encountered due to the inherent operation of an oil filter by-pass valve which is designed to open when the oil filter becomes sufficiently clogged to effect a pressure drop thereacross, usually approximating from 12 to 15 psi. Such by-pass operation ensures that a clogged filter will not prevent oil from reaching the engine nor will it rupture or spill contaminates into the engine. When a large volume oil manifold is used downstream of the filter, as is common with engines having several cylinders with piston cooling jets, the oil pump will strive to force oil through the filter quickly to thus fill the volumes downstream of the oil filter. The cooling jets, meanwhile, tend to drain oil out of the manifold while the oil pump is attempting to fill it.
Frequently, depending on oil temperature which determines oil viscosity, the oil passing through the filter will build-up a sufficient pressure drop thereacross to activate the by-pass valve to thus circumvent oil around the filter. When such a condition occurs, the crankshaft and rod bearings will be subjected to contaminants, thus resulting in the wear and possible failure thereof.
Various prior art apparatus and methods have been proposed to overcome the above problems but cannot always be employed on all engines and are also, by nature, complex and costly to manufacture and install. One such method utilizes a "pre-lube" pump which is driven by an auxiliary motor normally powered by a D.C. electrical source, such as a standard battery. Another method employs an auxiliary pump that runs continuously, being powered by an A.C. electrical source, so that the engine may be fired at any time.
Engines employing cooling jets thereon suffer from lubrication difficulties of another kind when they are running at low idle and the oil is hot. In particular, the oil pressure in the system will begin to drop with decreased engine speed, after the pump pressure by-pass valve closes. While idling, the pump must supply enough oil to satisfy the requirements of the piston cooling jets, which are not needed at idle, plus the requirements of all of the bearings employed in the engine. As bearings wear, their clearances increase to thus decrease oil pressure while increasing oil flow.
Such decrease in oil pressure will ultimately result in engine shut-down, on engines which employ a low oil pressure shut-off apparatus thereon, or eventual engine damage from oil starvation in engines which do not employ such an apparatus thereon. The most commonly used method for overcoming this problem is the use of a pump with a sufficiently large capacity to make the probability of oil starvation remote. The latter method is costly and results in excessive power consumption by the oversized pump which is not required during most phases of engine operation.